The problem with gender, is that heterosexual and homosexual people are sexist in their sexual attractions, so they will treat people differently based on their gender when it comes to sexual attraction. Thus, a topic of discussion appears where non would be had if they didnt felt sexually attracted to the new co worker.
It's easy, if they were asexual or homosexual this wouldnt happen. If they were all bisexual, this would happen with all co-workers.
Homosexuality and heterosexuality are sexist inherently (if we take sexism as treating people differently because of their sex ). Which is a bit funny in the context of this discussion.